You're filling in an application, you attach the PDF, and the portal refuses it: maximum file size 2 MB. Many government, university and job portals cap uploads at a few megabytes, and a document that looks perfectly ordinary can be ten times over.
The instinct is to throw the file at the first compressor you find. That sometimes works, but it can also leave you with blurry stamps, unreadable signatures, or a file that's barely smaller. It's faster to spend one minute working out why the file is big, because each cause has a different, and usually better, fix.
Step 1: a one-minute diagnosis
Open the PDF and note two things: the file size and the number of pages. Divide one by the other.
| Size per page | What it usually means |
|---|---|
| Under about 100 KB | A text document created on a computer. Already efficient; the problem is the number of pages. |
| About 300 KB to 2 MB | Scanned pages or pages built from phone photos. |
| Most pages small, file still huge | One or two pages hold an enormous image, often a pasted photo or an unscaled logo. |
Then try to select a sentence with your mouse. If you can, the text is real and the file was created digitally. If the whole page highlights as one block, or nothing highlights at all, you're looking at pictures of pages.
Step 2: apply the fix that matches the cause
Cause: the document was scanned at high settings
Office scanners often default to 300 dpi in full colour, which is more than a text document needs. For comparison, we produced the same five-page document two ways:
- 300 dpi colour, a common scanner default: 5.71 MB
- 200 dpi greyscale, the same pages: 785 KB
If you still have the paper and access to the scanner, rescanning at 200 dpi in greyscale is the cleanest fix; plain black text can go lower still in black-and-white mode. If you only have the file, compress it. On that same 5.71 MB scan, our Compress PDF tool's Balanced level produced 259 KB with the text still clear on screen.
Compress PDF Built for scanned documents. Pages become images, so text stops being selectable.
Cause: the PDF was made from phone photos
Photographing documents is quick, but each phone photo is typically several megabytes, and the PDF simply inherits their size. The fix is to shrink the photos before building the PDF.
An A4 page shown at 150 dpi, which is plenty for reading on screen, needs about 1240 × 1754 pixels. In our test, a 4.69 MB photo resized so its long edge was 1600 pixels and saved at JPG quality 80 came out at 274 KB, over 90% smaller, and still sharp at page size. Do that for each photo and a ten-page document drops from dozens of megabytes to a few.
Image Compressor Make the file smaller without making the picture worse.
JPG to PDF Collect several images into one tidy PDF document.
Cause: a Word document with large pictures
Word stores pasted photos at full resolution unless told otherwise, and the PDF keeps them. Compress the pictures in Word before exporting (Picture Format → Compress Pictures), then export again. Our guide on compressing a PDF without losing quality walks through the exact settings, and why rescanning-style compressors are the wrong tool for this kind of file.
Cause: more pages than the portal actually needs
Scanning a whole passport or a full bank statement when the form asks for one page is surprisingly common. Re-read what's being requested. Extracting just the required pages is lossless and often solves the problem outright.
Split PDF Pull out just the pages you need, or separate every page into its own file.
Cause: a long text document that's still over the limit
If the file is text-based and already around 50–100 KB per page, compression won't achieve much. The file is big because it's long. Check whether the portal accepts several files, and if so split the document into parts, such as “Report – part 1 of 2”. If it doesn't, contact the organisation; a size cap that can't hold the document they asked for is their problem to solve.
Hitting an exact target
Work backwards from the limit. Divide the maximum size by the number of pages to get a budget per page, then pick the setting that fits. From our five-page scan test, per page:
| Compress PDF level | Approx. size per scanned page | Pages under 2 MB | Pages under 5 MB |
|---|---|---|---|
| Original 300 dpi colour scan | 1.1 MB | 1 | 4 |
| Light | 130 KB | 15 | 38 |
| Balanced | 52 KB | 39 | 98 |
| Maximum | 31 KB | 66 | 167 |
Start with the gentlest setting that fits the budget. There's no prize for coming in far under the limit, and the person reviewing your application will appreciate being able to read the stamp.
Things that don't really help
- Zipping the PDF. A PDF's contents are already compressed, and scanned pages are stored as JPEG images, which barely shrink further. Many portals won't accept a ZIP anyway.
- “Printing” to PDF. Results are unpredictable. The file can come out larger, and links and bookmarks are lost along the way.
- Saving as PDF/A. The archival format embeds every font in full, so it can make the file bigger, not smaller. Only use it if it's specifically requested.
Before you upload
- Open the compressed file and read the smallest text at 100% zoom: stamps, signatures, reference numbers.
- Check the page count matches what you intended to send.
- If an upload fails for no obvious reason, try a short file name using English letters and no spaces. Some portals are fussier about names than they admit.
- Keep the original, full-quality file somewhere safe.